The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.
1. Field of the Invention
This invention relates to altering rings of polyhedral oligomeric silsesquioxanes (POSS) and more particularly to opening and/or expanding such rings to form other species thereof.
2. Description of Related Art
Recent art in the silsesquioxane field has taught processes for the chemical manipulation of the organic functionalities (substituents, e.g., denoted by R) contained on the silicon oxygen frameworks of polyhedral oligomeric silsesquioxanes (POSS). While these methods are highly useful for varying the organic functionalities contained on POSS molecules, they do not offer the ability to cleave and/or manipulate the silicon-oxygen frameworks of such compounds. Thus, these methods are of no utility for transforming the multitude of readily available polyhedral oligomeric silsesquioxanes systems into useful compounds that can be subsequently utilized for a multitude of catalysis and material applications.
Earlier art has reported that bases (e.g., NaOH, KOH, etc.) could be used to: (1) catalyze the polymerization of polyhedral oligomeric silsesquioxanes into partly networked resins, (2) convert polysilsesquioxane resins into discrete polyhedral oligomeric silsesquioxane structures, and (3) catalyze the redistribution of selected fully condensed polyhedral oligomeric silsesquioxane structures into other related fully condensed polyhedral oligomeric silsesquioxane structural types. While the base assisted/catalyzed method does afford the manipulation of silicon-oxygen frameworks, it is not effective at selectively producing incompletely condensed frameworks from completely condensed species. This limitation results from the intolerance of the silicon-oxygen framework present in polyhedral oligomeric silsesquioxanes to base.
Accordingly there is need and market for a method for opening and/or substituting on POSS rings that overcomes the above prior art shortcomings.
There has now been discovered a method that rapidly and effectively opens the silicon-oxygen frameworks of POSS compounds to produce species that can subsequently be converted to various functionalized POSS compounds.
Broadly the present invention provides a method for selectively opening rings of polyhedral oligomeric silsesquioxane (POSS) compounds to form functionalized derivatives which includes reacting [(RSiO1.5)n]xcexa3# (where R=aliphatic, aromatic, olefinic, alkoxy or siloxy or H and n=4-24) with an acid to form POSS species bearing one or more functionalities suitable for polymerization, grafting or catalysis. In such method, xcexa3 and # are as defined below and the acid is selected from the group of HBF4/BF3, CF3SO3H, ClSO3H, CH3SO3H, H2SO4, HClO4 and combinations thereof. Also provided are the POSS species formed by the above inventive method.
The invention further provides a method for expanding rings in polyhedral oligomeric silsesquioxane (POSS) compounds which includes, reacting [(RSiO1.5)n(R(OH)SiO1.0)m]xcexa3# where n=1-24, m=1-12 with Y2SiR1R2 silane reagents to obtain at least one expanded POSS ring in [(RSiO1.5)n(R1R2SiO1.0)i]xcexa3#, where R, R1 and R2 are aliphatic, aromatic, olefinic, alkoxy, siloxy or H, Y is halide or amine, n is 4-24, and j is 1-10. Again xcexa3 and # are as defined below Also provided are the POSS species formed by such inventive method.
For the purposes of explaining this invention""s processes and chemical compositions the following definition for representations of nanostructural-cage formulas is made:
Polysilsesquioxanes are materials represented by the formula [RSiO1.5]∞ where ∞=degree of polymerization within the material and R=organic substituent (H, cyclic or linear aliphatic or aromatic groups that may additionally contain reactive functionalities such as alcohols, esters, amines, ketones, olefins, ethers or halides). Polysilsesquioxanes may be either homoleptic or heteroleptic. Homoleptic systems contain only one type of R group while heteroleptic systems contain more than one type of R group.
POSS nanostructure compositions are represented by the formula:
[(RSiO1.5)n]xcexa3# for homoleptic compositions
[(RSiO1.5)n(RSiO1.5)m]xcexa3# for heteroleptic compositions
[(RSiO1.5)n(RXSiO1.0)m]xcexa3# for functionalized heteroleptic compositions
[(RSiO1.5)n(RSiO1.0)m(E)j]xcexa3# for heterofunctionalized heteroleptic compositions
[(XSiO1.5)]xcexa3# for homoleptic silicate compositions
In all of the above R is the same as defined above and X includes OH, Cl, Br, I, alkoxide (OR), acetate (OOCR), peroxide (OOR), amine (NR2) isocyanate (NCO), and R. The symbol E refers to elements within the composition that include (silanes and silicones e.g. SiR2, SiR2OSiR2OSiR2), (metals and nonmetals e.g. CrO2, PO2, SO2, NR) The symbols m, n and j refer to the stoichiometry of the composition. The symbol xcexa3 indicates that the composition forms a nanostructure and the symbol # refers to the number of silicon atoms contained within the nanostructure. The value for # is the sum of the lettered substituents in a compound e.g m+n or m+n+j. It should be noted that xcexa3# is not to be confused as a multiplier for determining stoichiometry, as it merely describes the overall nanostructural characteristics of the POSS system (aka cage size).
By xe2x80x9cstrong acidxe2x80x9d, as used herein, is meant one with a pKa number ranging from xe2x88x927 to 5 and is inclusive of superacids which cannot be assigned pKa values but which are characterized by Hammett acidity values H0 that range from 30 to 2.0 with the preferred range being 8-16.
Thus the present invention discloses methods that enable the selective manipulation of the silicon-oxygen frameworks in polyhedral oligomeric silsesquioxane (POSS) cage molecules. It is desired to selectively manipulate the frameworks of POSS compounds because they are useful as intermediate-chemical agents that can be further converted or incorporated into a wide variety of chemical feed-stocks useful for the preparation of catalyst supports, monomers, and polymers wherein they impart new and improved thermal, mechanical and physical properties to common polymeric materials.
Further the present invention teaches processes that enable the manipulation of the silicon-oxygen frameworks (aka. the cage-like structure) of common polyhedral oligomeric silsesquioxane (POSS) compounds [(RSiO1.5)n]xcexa3# (where R=aliphatic, aromatic, olefinic, alkoxy, siloxy or H and n=4-24) into new POSS species bearing frameworks with functionalities (e.g. silanes, silylhalides, silanols, silylamines, organohalides, alcohols, alkoxides, amines, cyanates, nitriles, olefins, epoxides, organoacids, esters, and strained olefins) for grafting, polymerization, or catalysis reactions.
Also in contrast to the prior art, the invention provides for the development of acid catalyzed processes that rapidly and effectively open the silicon-oxygen frameworks of polyhedral oligomeric silsesquioxanes to produce species that can subsequently be converted into stable incompletely condensed POSS-silanol and related functionalized POSS compounds. The use of acid reagents is desirable because the silicon-oxygen frameworks in polyhedral oligomeric silsesquioxanes are more tolerant of acids and hence will not as readily polymerize to form random networks, ladder polymers or other resinous systems. Acid reagents are also desirable in that their selectivity, rate of action, and the extent of reaction with fully condensed silicon-oxygen frameworks can be controlled through concentration, acid strengths (pH), and the chemical nature of the acid and its conjugate base. The nature of the solvent medium can also impart control over the cage opening process. Manipulation of these process variables allows for the optimization of conditions by which the silicon-oxygen frameworks of polyhedral oligomeric silsesquioxanes such as [(RSiO1.5)n]xcexa3# (where R=aliphatic, aromatic, olefinic, alkoxy, siloxy or H and n=4-24) can be selectively manipulated to produce new polyhedral oligomeric silsesquioxanes with functionalized structures. The polyhedral oligomeric silsesquioxanes produced from the acid treatment processes can be used directly as reagents in polymerizations or they can be additionally derivatized through reaction with a variety of organosilanes or organic reagents such as amines, phosphines, transition metals, or tin complexes to form a diverse number of new POSS chemical reagents.
Thus processes for the selective ring opening, stereochemical interconversion, expansion and reduction of the silicon oxygen frameworks in polyhedral oligomeric silsesquioxanes (POSS) to form new polyhedral oligomeric silsesquioxane chemical species have been developed. The selective ring-opening and stereochemical interconversion processes principally utilize strong acids (e.g., HBF4/BF3, CF3SO3H (trifluoromethanesulfonic acid), ClSO3H (chlorosulfonic acid), CH3SO3H (methanesulfonic acid), H2SO4 (sulfuric acid), HClO4 (perchloric acid), etc.) to react with the silicon-oxygen-silicon framework""s (Sixe2x80x94Oxe2x80x94Si) bonds. Conditions in the processes can be controlled so that the Sixe2x80x94Oxe2x80x94Si frameworks are selectively cleaved to afford species containing Sixe2x80x94X bonds where X is the conjugate base of the respective strong acid (e.g., X=F, CF3SO3, ClSO3, HSO4, ClO4) or where X=OH. The resulting new polyhedral oligomeric silsesquioxane species can then undergo additional chemical manipulations, such as cage expansion or reduction to ultimately be converted into POSS-species bearing one or more functionalities suitable for polymerization reactions.